Hard shelled gelatin capsules have a disadvantage in that the cap and body parts can be opened and rejoined without the disruption becoming externally visible.
Capsules which are telescopically joined have only a partial overlap of the cap side wall with the body side wall. This allows for gripping and withdrawal of the body part thereby making separation relatively easy.
One of the ways utilized to seal the capsule components to inhibit this easy separation is by banding. This process uses a gelatin solution which is rolled on the capsule at the juncture between the body and cap lip to form a band. While banding is successful against attempts at physical separation of the cap and body of the capsule, it is susceptible to disruption in the same way that the unmodified shell capsule components are.
Various attempts have been made to seal the body and head of the capsule directly to each other by means of a so-called "sealing fluid."
Prior art for capsule sealing is contained in the following patents:
U.S. Pat. No. 3,071,513, issued Jan. 1, 1963 to H. R. DeBoer et al. which discloses a sealing fluid comprising a dispersion of an air-drying hydrophilic, film-forming polymer in an organic solvent. The application of the sealing fluid was by dipping the capsules.
U.S. Pat. No. 3,159,546, issued Dec. 1, 1964 to J. R. Kane, discloses a liquid sealant consisting of three components containing by weight from about 1 to 41/2 parts, preferably 3 to 41/2 parts, of acetone; from about 11/2 to 2 parts, and preferably 11/4 to 2 parts, of water; and from about 3/4 to 21/4 parts, and preferably about 3/4 of a part, of ethyl acetate.
U.S. Pat. No. 2,924,920, issued Feb. 16, 1960 to Elly T. Margolis, discloses a three components mixture containing a polyhydric alcohol, an alcohol and water. This composition is used to seal capsules by a swelling technique. The process is designed to avoid solvent penetrating the overlap between capsule body and cap.
French Pat. No. 2,118,883, issued June 6, 1975 to Green Cross Corporation, discloses the use of alcohol and water in an enteric coating process.
U.S. Pat. No. 4,539,060, issued to Fritz Wittwer and Ivan Tomka on Sept. 3, 1985 describes sealing by contacting the capsules with a stream of sealing fluid which is then positioned between the overlap of the cap and body parts by capillary action. Excess sealing fluid is then drained of excess fluid and the capsule parts with the fluid in place is subjected to thermal energy. Several sealing fluids are suggested in this patent including aqueous solutions of salts, cations and ions, water and polymer solutions or emulsions.
European Patent Application Ser. No. 152,517 discloses the use of thermal energy in conjunction with a mixture of alcohol and water to provide a seal between the cap and capsule body wherein as with the Wittwer et al. patent, the fluid is positioned by capillary forces between the cap and the capsule body and subsequently heated in situ.
The tamper-resistant sealing prior art, therefore, is generally of two types. That which requires the addition of an added element which seals the overlap between the capsule cap and body and those which by the choice of appropriate solvents unite the cap and body. However, it has been found that, when using a sealing agent within the overlap of the cap and body portions without the application of heat, the seal is generally insufficient to maintain a liquid medicament in the capsule. Also, when heat is applied, numerous localized distortions of the capsule wall occur, so that further handling is extremely difficult.